This invention relates generally to a fingerprint processing apparatus and more particularly to one that is capable of generating a full roll fingerprint image by means of an optical scanning technique.
Optical scan finger image processing apparatus capable of generating a fingerprint image that can be encoded into machine readable signals are known in the art. Examples of such apparatus are described in U.S. Pat. Nos. 4,553,837, 4,544,267, 4,537,484, 4,322,163 and 4,152,056. These patents indicate techniques for providing an optical scan of a finger held against a transparent platen in which an interrogating light beam is scanned across the finger to provide a reflected modulated light beam which is focused onto an array of photo-electric transducers to provide a series of electrical signals that carry fingerprint information. Some of these patents use a flat platen. Others used a curved platen in order to get a larger portion of the fingerprint than a flat platen provides.
It is often desired to provide an optically developed fingerprint that is a full roll fingerprint of the sort that is obtained by rolling a finger across an ink pad from nail edge to nail edge and then rolling the inked finger across a card.
In order to provide as much finger contact as possible on the concave surface of the curved platen, the optical fingerprint apparatus may employ multiple curved platens having different dimensions to accommodate fingers of different thickness and different nominal radius. Yet, even with multiple diameter curved platens, a finger that fits within the closest approximation will not fully touch from nail to nail. The reasons for this in part are because the range of finger sizes are continuous while the number of curved platens that can be provided are limited and in part because the finger surface is not a perfect circular cylinder.
Accordingly, the purpose of this invention is to provide a technique and an apparatus to permit obtaining a full nail-to-nail roll fingerprint from an optical scanning apparatus employing a platen.
A related purpose of this invention is to provide this full roll technique with a mechanism that is sufficiently simple and straightforward in use so that it will provide accurate results on a consistent basis with a large number and wide variety of fingers.
It is important that the apparatus takes into account not only the variability of the population of fingers but also the variable ability of people to interface with a machine.